These are (apparently) the decisions that follow you over to Mass Effect2
MAJOR SPOILERS FOR THOSE WHO HAVE NOT PLAYED ME 1 !!!!!!
The decision to save either Kaidan or Ashley.
Whether or not the player kills Wrex on Virmire.
Whether or not the player decides to save the Citadel Council
The player's choice of love interest
Whether the player spares or destroys the Rachni Queen at Peak 15
The player's treatment of Conrad Verner (The Fan at the Citadel)
Whether or not the player completed the UNC: Asari Diplomacy sidequest.
Whether the player chose to allow the Alliance to conduct experiments on Nirali Bhatia's body
Aside from this if you finished largely on the Paragon or Renegade side, you get an immidiate boost in those aspect, which can affect some early quests.
Also, the higher the level you are, the more resources/cash you get from the start to spend on research, etc.